FINAL Flashcards
UAS stands for
Unmanned Aircraft Systems
A UAS consists of
1) an aircraft with no pilot on board,
2) a remote pilot station, 3)
a command and control link, and
4) a payload specific to the intended application/operation
Other names for UAS
drone
Unmanned Aerial Vehicle
Remotely Piloted Aircraft System
Unmanned Aerial System (less common)
Unpiloted Aircraft System (less common)
A UAS for civil applications is commonly referred to as a small unmanned aircraft system (sUAS) weighing less than
55 pounds
the two types of sUAS
Fixed-wing
Multirotor
Fixed-wing drones have better _____ but are __________
battery efficiency, harder to fly
Multirotor drones fly by
changing the speed of the rotors so that the thrust generated is greater than, equal to or less than the forces of gravity and drag acting on the aircraft
The ______ regulates the rules for small UAS operations under 14 CFR 107
FAA
The maximum allowable altitude for UAS is
400 ft
Maximum speed for UAS is
100 mph
Effective 2021, FAA now requires most UAS to be equipped with
remote ID
How long is UAS certificate of registration good for
3 years
To operate the controls of a UAS, you need a __________ or ____________
remote pilot certificate, be under the direct supervision of a person who holds such a certificate
There are two checklists for flying a UAS, one to be done ______ and the other to be done ________
before going out to fly, before taking off
The first item on the pre-going out to fly checklist is
Check the NOAA Aviation Weather Center website for weather conditions
A best practice for capturing quality drone data is _________ because __________
Fly within 2 hours of local solar noon, Shadows are the shortest and solar radiation intensity is the highest
Note: 12 pm is NOT solar noon
Drone images should have _____ % overlap
75
True or false, ALL aerial images contain geometric distortions
True
Ways that aerial images can be distorted
Shape
Size
Scale
Geometric distortions are created due to _______ errors and _______ errors
systematic, random
Examples of Systematic Distortions are
Earth rotation
Earth’s curvature
Atmospheric refraction
Topographic effects
Relief displacement
Examples of Random Distortions are
Changes in flight altitude
Changes in flight attitude (roll, pitch, yaw)
Changes in velocity
Relief displacement
Tall objects are displaced away from the center of the air photo
Geometric Correction
putting pixels in their proper planimetric (x, y) map locations i.e. real-world coordinates referenced to a map projection
A geometrically corrected image is often referred to as
an orthophoto
Geometric correction of an air photo is also known as
Georeferencing
Georectification
Image-to-map rectification
Geometric transformation
Geometric correction requires 4 basic steps:
1) Choose a source
2) Select ground control points (GCPs)
3) Image transformation
4) Accuracy assessment
The best source for georeferencing is
Google Earth Pro
Examples of Good GCPs
building corners, street corners, large trees, landmarks
Examples of Poor GCPs
cars, rocks, shoreline of a beach, center of a field
GCPs must be distributed…
evenly across the unreferenced image, starting from edges and working towards the center
A minimum of ___ GCPs is required
3
More GCPs =
better fit
Accuracy Assessment incorporates
the total root mean square error (RMSE)
The lower the overall RMSE,
the better the fit is
_______ is the most important physical quantity in remote sensing
Radiance
Radiance indicates
how much of the energy emitted, reflected, transmitted or received by a surface will be finally received by a remote sensor
Remote sensors measure radiance in a different range of wavelengths and then convert radiance signals to
digital numbers (DNs)
The DN of each image pixel corresponds to
the average radiance measured electronically over the ground area corresponding to that pixel
Theoretically, there is a ________ between radiance measurements and surface reflectance
direct linear relationship
reflectance
proportion of radiation reflected from surface objects relative to the total amount of incident energy
The ____ - ____ relationship can be used to perform radiometric calibration for air photos
radiance-reflectance
Assumptions of Empirical Line Calibration
the darkest object in an image does not reflect or emit any radiation. DN = 0 represents rλ = 0.
the brightest object in an image does not saturate DN (DN < 255)
radiance measurements made by a sensor have a perfect positive linear relationship with surface reflectance
The pinhole camera was later replaced by
the
simple lens camera
The simple lens camera introduced the adjustable
diaphragm and shutter
A diaphragm (a.k.a. aperture stop) controls…
the amount of light reaching the film
A shutter is a device that
allows light to pass for a determined period
The camera lens is an optical device that
consists of a curved (convex) material that allows light to pass through. The lens bends the light, reassembles the light reflected from the scene, and forms an image on the sensor
the process called focus
Moving the lens closer or further from the sensor to channel the light to recreate the image clearly
focal length
the distance from the lens at which parallel light rays are focused to a point
Shutter controls the duration of exposure (t), also known as
shutter speed
Diaphragm controls the diameter (d) of the lens opening during exposure, also known as
aperture
Exposure is the amount of…
energy exposed onto the sensor per unit sensor area
In photography, aperture is expressed in f-numbers, known as
f-stops
A small fstop (e.g., f/1.4) means a
large aperture (wider opening), while a large f-stop (e.g., f/32) means a small aperture (smaller opening)
Aperture size has a direct impact on the ______ of a photograph
brightness
A smaller f-stop allows _________ into the camera
more light
Depth of Field (DoF)
the range of distance of the image that appears acceptably sharp
A small f-stop (e.g., f/1.4) makes the foreground objects ______ but the background ______
sharp, blurry
A large f-stop (e.g., f/32) aka small aperture brings _______ in focus
all foreground and background objects
True/false, both aperture and shutter speed control the amount of light that comes into the camera
True
A slower shutter speed lets in ______ light into the camera
more
units for aperture
f-stops
units for shutter speed
seconds
If the shutter speed is slow (e.g., 1/2 s), it can create an effect called
“motion blur”, where moving objects appear blurred along the direction of the motion
With longer shutter speed, images appear brighter/darker?
brighter
A fast shutter speed ______ the action in the image
freezes
ISO
the camera’s sensitivity to light
A lower ISO value means ______ sensitivity to light, while a higher ISO means ______ sensitivity
less, more
ISO is a camera setting that will
brighten or darken a photo
As the ISO number increases, the photo will become
progressively brighter
True/false, A photo at ISO 400 is twice brighter than ISO 200
True
True/false, You should only raise your ISO when you are unable to brighten the photo via shutter speed or aperture instead
True
A photo taken at too high of an ISO will
show a lot of grain
when a high ISO is necessary
when you really need to freeze the action in a photo and therefore need a fast shutter speed
The aperture value and shutter speed are ________ proportional
inversely
True/False, In aerial photography for remote sensing and photogrammetry purposes, the rule of thumb is to slightly underexpose your photos
True/False, Overexposure is irreversible
True
Filters are
transparent materials that, by absorption or reflection, eliminate or reduce the energy reaching a film in selected portions of the spectrum
A low-pass filter
allows lower wavelengths to pass through but blocks higher wavelengths
A high-pass filter
absorbs energy below a certain wavelength
A band-pass filter
absorbs all other wavelengths except a specific band
A band-stop filter
absorbs energy for a specific range of wavelengths but allows other wavelengths to pass through
a ______ filter is the most popular colored filter used for black and white photos
yellow
A single-lens camera uses ______ bands
wide
A multi-lens camera uses ______ bands
narrow
Bands on a ______ camera suffer from data contamination from neighboring bands
single-lens camera
Photogrammetry is
the science and technology of obtaining reliable spatial measurements and geometric information about surface objects and phenomena
True/False, Remote sensing deals with 2D satellite imagery whereas Photogrammetry not only works on 2D imagery, but also more complex 3D models
True
True/false, Photogrammetry uses an imaging system rather than collecting data in different wavelengths
True
two main branches of Photogrammetry
metric and interpretive
Metric Photogrammetry
makes precise measurements and evaluates exact sizes, shapes, positions, distance, angles, areas, volumes, and elevations of surface features
Interpretative Photogrammetry
deals in identifying surface objects and judging their significance
Aerial photographs are classified as either
vertical or oblique
Vertical photo
an aerial photo taken by a camera looking straight down at the ground
Oblique photo
an aerial photo taken at an angle
Low oblique photo
the horizon is not shown
High oblique photo
the horizon is always visible
Nadir
the location on the ground that lies directly below the camera
Principal Point
the center of a vertical photo – found by the
intersection of lines connecting opposite and diagonal fiducials
Nadir is equal to Principal Point in what type of photos
vertical
True/False, in oblique photos, it’s possible for the nadir to not be shown
True
Why when elevation changes, the distance between a-b appears shorter than the distance between c-d (higher elevation) on the photo
Relief Displacement
Relief displacement is the
shift in an object’s image position caused by its elevation above a particular datum
If an air photo is ________, the displacement of objects in the air photo is in a direction radial from the principal point (or nadir)
vertical
All matter with a temperature greater than absolute zero (0 K) emits
thermal energy, or heat
Thermal radiation is generated when
heat from the movement of charges in the material is converted to EMR
The ______ the particles move, the greater the kinetic energy and the greater the object’s thermal radiation
faster
Temperature is the
measure of the average kinetic energy of the particles in a substance
True/False, All objects on Earth’s surface emit thermal radiation
True
Why we can use thermal sensor to measure an object’s surface temperature
There is a direct relationship between temperature and the amount of TIR energy emitted per unit area
Why does TIR band imagery have a lower spatial resolution than visible and NIR band imagery?
thermal uses longwave energy, so there is less energy for the sensor to pick up. TIR sensor needs a larger IFOV to ensure enough energy reaches the sensor in order to make reliable measurements
what is directly measured by a TIR sensor
M, or the energy that an object emits per unit area
why the calculation of LST is much more complicated than the Stefan-Boltzmann Law equation
Need to calculate emissivity
The emissivity, ε, of a surface material is
its effectiveness in emitting energy as thermal radiation
a blackbody has an emissivity of
1
Real objects radiate less thermal radiation than a
blackbody and therefore are called ________
graybodies
Emissivity is the ratio of the thermal radiation emitted from a surface material to the radiation from a _________ at the same temperature
blackbody
To calculate LST using Ladsat/MODIS/ASTER imagery, you need to know the
Multiplicative Scale Factor and Additive Offset
Cause of urban heat island
Building materials absorb long wave radiation during the day
and have lower rates of radiant cooling during the night
Urban Heat Island (UHI) Effect
urban areas have higher temperature in comparison to the surrounding rural areas
Boundary layer UHI is measured by
weather balloons
Surface layer UHI is measured by
rooftop weather station
Canopy layer UHI is measured by
weather station at 2-m above the ground
Surface UHI is measured with
remotely sensed thermal infrared imagery
yellow has no
blue
magenta has no
green
cyan has no
red
Depth of Field (i.e. how much of image is sharp) increases as _________ increases
aperture
All the objects in an aerial photo need to be in focus, which means a ______ aperture/______ f-stop should be used
small, large
The DLS sensor on a drone _______ so that ________
collects incoming solar radiation, radiance can be converted to reflectance
First item on pre-takeoff checklist
Place the UAS on a flat surface and make sure there is no dirt, rock, and debris underneath the UAS
